The discovery of lyotropic fully aromatic polyaramides, as described in U.S. Pat. No. 3,671,542, has generated a great deal of interest in ultrahigh strength, high modulus fibers. Polyaramides have been commercialized under the trademarks TWARON, by Akzo Fibers, and KEVLAR, by DuPont.
After the discovery of the aforementioned polyaramides, extensive research began to find other polymers, such as polyamides and polyesters, which could be melt processed. While a variety of thermotropic liquid crystalline polyesters were developed as a result of such research, only very few polyamide compositions are known which are thermotropic liquid crystalline and display melting points prior to decomposition.
Takayanagi et al., in J. Macromol. Sci.-Phys., B17(4), 591-615 (1980), teach certain lyotropic wholly aromatic polyamides, such as poly(p-phenylene terephthalamide), poly-p-benzamide and their block copolymers with blocks of nylon-6 or nylon-6,6. These materials were indicated as being sparingly useful for blending with a matrix of nylon-6 or nylon-6,6.
H. Ringsdorf et al., in Makromol. Chem. 188, 1431-1445 (1987), describe aromatic polyamides with disc-like mesogens in the main chain which can be prepared from tetra-substituted hydroquinones and derivatives of 1,4-phenylenediamine.
J. M. G. Cowrie et al., in British Polymer Journal 20 (1988) 515-519, describe thermotropic liquid crystalline main chain polyamides containing diazo-18-crown ether units, and, in Polymer, 29 (1988) 1128 and following, describes analogous work using a cyclooctyl ring as a flexible spacer. The latter spacer was useful in promoting a liquid crystalline phase, whereas the former spacer was not.
More recently, U.S. Pat. No. 5,070,155 describes semiaromatic copolyamides and copolyester-amides formed by reaction of (a) an aliphatic polyamide, (b) an aromatic aminoacid and/or an aromatic hydroxy acid, and (c) a stoichiometrically equivalent mixture of a diacid selected from the group consisting of the aliphatic diacids containing from 6 to 10 carbon atoms and terephthalic acid and 4,4'-dihydroxy-biphenyl. Thus, this patent document exclusively teaches the use of para-substituted aromatic reagents.
Certain examples also exist in the literature of thermotropic, liquid crystalline poly(ether-amide) compositions, as contrasted to thermotropic liquid crystalline copolyamide compositions: A. C. Griffin et al., Mol. Cryst. Liq. Cryst. Vol. 82 (Letters), pp. 145-150 (1982); M. Schmuki et al., Makromol. Chem. 190, 1303-1308 (1989); and T. Uryu et al., Polymer Journal, Vol. 21, pp. 977-986 (1989).